The nature of long-chain branching in natural rubber (NR) from Hevea brasiliensis was analyzed for NR purified by enzymatic deproteinization in the latex state followed by acetone extraction in the solid state to remove the proteins and neutral lipids, respectively. The treatment of purified NR in a toluene solution with a polar solvent, such as methanol or acetic acid, resulted in a clear decrease in the molecular weight, gel content, and Huggins' constant; this was caused by the decomposition of branch points in the purified rubber. This finding clearly showed that long-chain branching in the purified NR was mainly derived from the association of phospholipids linked with both terminal groups in the rubber chain via hydrogen bonds. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 3645-3650, 2010